The present invention relates to a control technology of a variable valve operating mechanism that performs a valve timing control and a valve lift amount control, independently, of at least one of an intake valve and an exhaust valve.
There have been practically used various kinds of variable valve operating mechanisms that control valve timing or a valve lift amount of an intake valve or an exhaust valve to an optimal control amount.
In order to further improve power and exhaust gas purification performance of an engine, there has been developed a mechanism that variably controls both of valve timing and a valve lift amount of an intake valve or an exhaust valve.
In Japanese Unexamined Patent Publication 2000-328971, a valve timing (opening and closing timing) variable mechanism and a valve characteristic switching mechanism of an intake valve are disposed together at an intake side camshaft, so that both of valve timing and a valve lift amount of the intake valve can be changed, thereby variably controlling the valve timing and the valve lift amount for each operating region determined based on a rotation speed and load of an engine.
The above conventional variable valve operating mechanism performs the valve timing control and valve lift amount control of the intake valve independently, and each control range is set so that the engine performance (operating performance, exhaust gas purification performance and the like) can be increased to a maximum depending on each control characteristic. However, in a case where the valve timing control and the valve lift amount control are performed together, for example in a partially loaded medium speed region, if the valve timing is controlled to an advance angle side and the valve lift amount is controlled to a large lift amount side, respectively, the valve lift amount in the vicinity of the top dead center of a piston becomes extremely large, thereby possibly causing interference between the intake valve and the piston.
If a stopper and the like are used to mechanically limit a maximum advance angle value of the valve timing variable mechanism and the valve lift amount of the valve characteristic switching mechanism of the intake valve, so as to avoid an excessive increase of valve lift amount in the vicinity of the piston top dead center, the control range is narrowed. Also, in the control of the valve timing and the valve lift amount in which there is no interference between the intake valve and the piston, an upper limit of control amount is limited. Therefore, it is impossible to obtain sufficient effects due to an increase of engine power and the improvement of exhaust gas purification performance by using both of the valve timing variable control and the valve lift amount variable control of the intake valve.
Note, in such a mechanism in which a valve timing control and a valve lift amount control of an exhaust valve are performed together, if the valve timing is controlled to a retarded angle side and at the same time, the valve lift amount is controlled to a large lift amount side respectively, there is a possibility of interference between the exhaust valve and the piston, thereby causing the same problem.
The present invention has been achieved in view of the forgoing problem, and has an object for, in a variable valve operating mechanism that uses both of valve timing control and a valve lift amount control of an intake valve or an exhaust valve but performs the valve timing control and the valve lift amount control, independently, expanding as wide as possible control regions of valve timing and a valve lift amount of at least one of the intake valve and the exhaust valve, while preventing interference of the intake valve or the exhaust valve with a piston, to thereby increase the engine performance to a maximum.
In order to achieve the above object, the present invention provides an apparatus and a method for controlling a variable valve operating mechanism that performs a valve timing control and a valve lift amount control of at least one of an intake valve and an exhaust valve, wherein a control range of one of the valve timing and the valve lift amount is limited in accordance with a control state of the other.
According to the above constitution, if, regardless of the control state of one of the valve timing and the valve lift amount of the intake valve or the exhaust valve, the other is controlled in accordance with an engine operating condition and, as a result, there is caused interference of the intake valve or the exhaust valve with the piston, the interference with the piston can be prevented by limiting the control range of the other.
The other objects and features of this invention will become understood from the following description with accompanying drawings.